iStock/Thinkstock(NEW YORK) -- Looking to cut costs when you travel? Farecompare CEO Rick Seaney sat down with ABC News to give his tips on how to save money when choosing what days to fly.

Here's what he had to say:

Are you a true cheapskate?

You are if you do this when traveling: You always use a carry-on to avoid the checked-bag fee. You pack a lunch from home so you don’t pay for airline meals. And first class? Hah! Nothing but economy for you.

But true cheapskates do one more thing; they fly on the three cheapest days of the week. For U.S. domestic travel, Tuesdays, Wednesdays and Saturdays are usually the least expensive days to fly.

It’s simple, really: Demand is low because who wants to start a vacation in the middle of the week? Everyone wants to fly Fridays and Sundays but you pay a price for popularity and those are usually the most expensive days to fly.

The good news is airlines have to fill up their planes every day of the week so they do the only thing they can for flights on unpopular days: They lower the fares.

These examples are for Los Angeles-to-New York flights in September, trips of about a week’s duration:

- Friday to Sunday: $365- Wednesday to Tuesday: $288

For transatlantic flights, the difference can be more startling and the rules a little looser: In general, weekdays are cheaper than weekends. Now check out these Boston-to-Dublin fares from United Airlines:

- Friday to Sunday: $581- Wednesday to Tuesday: $457

Time for some Saturday fares now. This example features Chicago-to-Atlanta routes:

- Friday to Sunday: $207*- Saturday to Saturday: $89

*There were cheaper fares for this itinerary, but only if the Sunday flight departed at 5 a.m. or earlier.

Is the rule on the "cheapest three days to fly" etched in stone? No.

It is usually true but not always, which is why I urge people to be as flexible as possible whenever shopping for airfares. If you can step back from a fixed itinerary and use tools to find cheap days to fly during specific months you’d like to travel, do this. It can save a significant amount of money. And isn’t that what being a cheapskate is all about?

Rick Seaney is the CEO of FareCompare, a website that curates the best deals on flights from around the world. Any opinions expressed in this column are solely those of the author.